Polycarbonate resin molded articles have been widely used as, for example, industrial transparent materials in the fields of electricity and electronics, machinery, automobiles, and the like or optical materials for lenses, optical disks, and the like because each of the articles is excellent in transparency and mechanical strength. When an additionally high mechanical strength is needed, a glass filler or the like is added to each of the articles to strengthen the article.
Glass fibers each constituted of glass generally called an E glass have been used as the glass filler. However, the refractive index of the E glass at a sodium D line (nD, hereinafter simply referred to as “refractive index”) is somewhat small, specifically, about 1.555, though, the refractive index of a polycarbonate resin is 1.580 to 1.590. Accordingly, when the glass filler is added to a polycarbonate resin composition in an amount needed for an increase in mechanical strength of the composition, the following problem arises: the resultant E glass-reinforced polycarbonate resin composition cannot maintain its transparency owing to a difference in refractive index between the filler and the polycarbonate resin of which the composition is formed, with the result that the composition cannot maintain its transparency.
In order to solve the problem above, various proposals have been made until now.
For example, (1) a polycarbonate resin composition containing a polycarbonate resin using a product of a reaction between a hydroxyaralkyl alcohol and lactone as a terminal stopper and a glass-based filler having a refractive index smaller or larger than that of the polycarbonate resin by 0.01 or less (see Patent Document 1), (2) a polycarbonate resin composition containing a polycarbonate resin, a glass fiber having a refractive index smaller or larger than that of the polycarbonate resin by 0.015 or less, and polycaprolactone (see Patent Document 2), (3) a glass composition obtained by incorporating ZrO2, TiO2, BaO, and ZnO into a glass filler composition at a specific ratio so that the refractive index of the composition is close to that of a polycarbonate resin (see Patent Document 3), and (4) a polycarbonate resin composition having good transparency and high mechanical strength, and containing a polycarbonate resin, a specific glass ingredient, and a glass filler having a refractive index smaller or larger than that of the polycarbonate resin by 0.001 or less (see Patent Document 4) have been proposed.
However, the polycarbonate resin composition in the above section (1) is not practical because of the following reasons: when the glass-based filler is added in an amount needed for an increase in mechanical strength of the composition, the difference in refractive index at such level is not small enough for the addition to exert its effect, and a raw material used for the production of the polycarbonate resin is too expensive.
The polycarbonate resin composition in the above section (2) involves the following problem: reductions in heat resistance and mechanical characteristics of the composition are inevitable owing to the presence of polycaprolactone, though, the glass fiber can maintain its transparency even when the glass fiber has a refractive index smaller or larger than that of the polycarbonate resin by 0.015 or less.
Unless the content of each of ZrO2, TiO2, BaO, and ZnO in the glass composition in the above section (3) is appropriately adjusted, the glass will devitrify. As a result, even when the glass composition has a refractive index equal to that of the polycarbonate resin, a polycarbonate resin composition containing the glass composition may be unable to obtain transparency.
Further, the document disclosing the polycarbonate resin composition in the above section (4) does not refer to flame retardancy. Accordingly, unless flame retardancy is imparted to the composition, fields where the composition can be used will be limited.    Patent Document 1: JP 07-118514 A    Patent Document 2: JP 09-165506 A    Patent Document 3: JP 05-155638 A    Patent Document 4: JP 2006-022236 A